Don't know what to do

I am in high school and I just started dating this guy about a week ago. I thought I liked him, so I said yes when he asked me out. He is really sweet and always texts me the nicest things but I realized that I don't like him as a boyfriend. I just want to focus on school and my future right now. I don't want to date him anymore, but he always talks about how he's so lucky to have me and how happy he is now. I am afraid that I could really hurt his feelings if we break up, but I don't want this relationship to be anything more than just friends. I can't stay with him but I need a nice way to end things before things get serious and without hurting him. Any advice would be very helpful, thanks.